L-amino acid, in particular L-lysine has been widely used as for animal feeds, as a raw material for medicines and in pharmaceutical industry, and produced by fermentation of the microorganisms of Corynebacterium genus.
Microorganisms of Corynebacterium genus, particularly Corynebacterium glutamicum is a Gram-positive microorganism that are widely used in L-amino acid production. The method of producing L-amino acids using the microorganisms of Corynebacterium genus is very important. So, there have been many attempts made to improve the method.
One of the attempts is to improve the microorganisms of Corynebacterium genus that produces L-amino acid by disrupting specific genes or attenuation expressing specific genes using a recombinant DNA techniques. For example, U.S. Pat. No. 6,872,553 discloses a method of producing L-lysine of microorganisms of Corynebacterium genus by fermentation which comprises the following steps: a) growing microorganisms of Corynebacterium genus having an attenuated DNA encoding phosphoenolpyruvate (PEP) carboxykinase (PCK) by one of the mutation method selected from the group consisting of insertion or one or more base pairs in the DNA, deletion of one or more base pairs in the DNA, transition or transversion of base pairs by introducing a nonsense codon in the DNA or having reduced phosphoenolpyruvate (PEP) carboxykinase (PCK) compared with microorganisms of Corynebacterium genus that are not attenuated; b) concentrating desired L-amino acid product in medium or cells; and c) separating L-amino acid.
In addition, many studies on how each gene involved in L-amino acids biosynthesis affects L-amino acid production by amplifying the genes to develop microorganisms of Corynebacterium genus have been conducted (Eggeling, Amino Acids 6, 261-272 (1994)). Also, microorganisms of Corynebacterium genus can be developed by introducing foreign genes from other bacteria. For example, Japanese Laid-off Patent Publication No. Hei 7-121228 discloses a method of producing L-glutamic acid and L-proline by culturing the microorganism of Corynebacterium genus or Brevibacterium genus that contain recombinant construct between DNA fragment having genetic information involving synthesis of citric acid synthase and vector DNA, and producing L-glutamic acid and L-proline from the cultures.
However, it is still required to produce a strain with enhanced L-lysine productivity, in spite of the above trials.